Alternator Bad Diode!?!??!?!

[turbohye]

Hey guys/ gals,
its been several years still checking the car for a bad short. Battery drains at a mere 3.5 milliamps. Brand new battery will be dead in a few days unless i drive it. Like i said, its been several years diagnosing while she sits parked in the garage.
Checked grounds, pulled console, fan relay, every damn bulb etc etc...
well... today, i was doing some test and again 3.5 being drawn on the multimeter....so i decided to disconnect the 1- wire from the alternator...
multimeter goes straight to 0.
Plugged the 1 wire back in (this wire has a clip but there are other wires that go to the alternator) and the multimeter goes back to 3.5
Does anyone know if this indicates a bad diode???? and if so, a new alternator would obviously solve this multi-year long endeavor!!??!?!?! lol please advise because im losing my patience..
ORRR by me disconnecting that 1 wire, did i just break the circuit and hence the multimeter showing 0... please tell me its the diodes...

Now i know there are multiple wires going to the alternator... most notable bolt into the the back of it.. however, this is that 1-wire that goes kinda on the side near the back...hard to explain but theres only 1 wire like it..

Anyone?!?!?! please help

 

[Jordan_J]

You could take the alternator off and take it in to a local parts store to get checked. Our machine will say if it's the diode that's bad.

 

[davelostmissing]

IMHO: 3.5 ma or 0.0035 amps should take a long time to discharge a fully charged 80 (guessing) amp-hour battery. Are you sure you don't have a charging problem?
I thought I read current body computers etc may draw 100ma on newer cars?

 

[mikestertwo]

IMHO: 3.5 ma or 0.0035 amps should take a long time to discharge a fully charged 80 (guessing) amp-hour battery. Are you sure you don't have a charging problem?
I thought I read current body computers etc may draw 100ma on newer cars?

Agreed. 3.5ma should not run down a battery in a couple of days. You have other issues.

 

[chopped39]

Agreed. 3.5ma should not run down a battery in a couple of days. You have other issues.

X2 3.5ma is not bad. newer cars have pcm's that stay awake for hours after car is shut off. And they pull alot more than that. Are you sure its not 3.5 amps. did you try pulling fuses.If not pull fuses one at a time till draw is gone. If it drops when a fuse is pulled check that circuit for problems.

 

[83ttypecooled]

Hi,
I must agree with the other guys. If you aren't reading the amp meter wrong,then just replace the alternator,and be done with it.

 

[salvageV6]

3.5ma isn't a bad diode, that's usually enough to light up the volts light dimly which should be more than 100ma. depending upon the diode.

3.5ma is low and safe.

Double check the meter reading and load test the alternator at a good store or shop.

 

[Steve V]

Hey guys/ gals,
its been several years still checking the car for a bad short. Battery drains at a mere 3.5 milliamps. Brand new battery will be dead in a few days unless i drive it. Like i said, its been several years diagnosing while she sits parked in the garage.
Checked grounds, pulled console, fan relay, every damn bulb etc etc...
well... today, i was doing some test and again 3.5 being drawn on the multimeter....so i decided to disconnect the 1- wire from the alternator...
multimeter goes straight to 0.
Plugged the 1 wire back in (this wire has a clip but there are other wires that go to the alternator) and the multimeter goes back to 3.5
Does anyone know if this indicates a bad diode???? and if so, a new alternator would obviously solve this multi-year long endeavor!!??!?!?! lol please advise because im losing my patience..
ORRR by me disconnecting that 1 wire, did i just break the circuit and hence the multimeter showing 0... please tell me its the diodes...

Now i know there are multiple wires going to the alternator... most notable bolt into the the back of it.. however, this is that 1-wire that goes kinda on the side near the back...hard to explain but theres only 1 wire like it..

Anyone?!?!?! please help

Hey Tony! My white T will do this also,I have not checked into it yet. If you unplug that alt and it goes to 0 I would start there.

 

[TurboJim]

The diode trio isnt connected in any way to the plug. Its connected to the output wire bolted to the rear of the alt. The alternator by design generates an AC voltage. The diode trio is designed to snip off the sine waves that go below 0 volts, leaving only the sine waves above 0 volts. The regulators job is to vary the stators magnetic field to keep that voltage in a certain range. The brown wire to the back of the alternator comes from the dash, the volts light to be exact. It is powered through the volts light bulb, and the regulator grounds this wire to turn the volts light on. Some vehicles use an "external sense" on the alternator which would be in that plug as well. Typically a red wire, and it generally comes from the point that the output wire terminates. The CS120 only uses the brown wire, and the voltage sense is done internally, unless you have added a volt booster or something.

A 3.5mA draw is nothing, and actually seems low. In the field on modern cars I shoot for under 50mA, so maybe you saw 3.5 AMPS and not milliamps? That would be excessive and kill the battery in 8 hrs or so. Does your car have a power antenna? Could the motor remain running intermittently? That would put you in the 3.5A ballpark.

 

[1qkgn]

Exactly What Jim Said

 

[turbohye]

actually, it could very well be 3.5 amps..(ill verify tonight)
last night, the car started fine. ( i had left that wire disconnected since i posted)

normally the battery would be dead in a matter of 8-12 hours..

Scanmaster showed 12.2 before cranking after sitting for 4 days.. I definately will have the alternator tested tomorrow at Autozone..

thanks for all your help guys.. Either the alternator is causing the issue, or GOD really doesnt want me to keep this car.. patience is running low.